Structural Flakeboards and Composites 3059 



Crystals formed in cement with no additives were needle-like and crisscrossed 

 (fig. 24-64 bottom). Addition of calcium chloride caused crystals to be better 

 defined and more conical in shape (fig. 24-64 top). 



Ahn and Moslemi (1980) concluded that the crystals interlock with wood 

 surfaces within cell lumens and elsewhere, and that when crystals butt against 

 wood they tend to grow into whatever cavities are present; if they abutt a flat 

 location they form flat ends (fig. 24-65). 



They found that addition of 0.5 percent sucrose interfered with hydration and 

 virtually prevented crystal formation (fig. 24-66 top). Addition of glucose 

 caused formation of a cloth-like mass of thin long fibers that contribute little to 

 strength development (fig. 24-66 bottom). 



DATA SPECIFIC TO SOUTHERN HARDWOODS 



Moslemi et al. '^ used a wood-to-cement ratio of 15:200 (by weight) to screen 

 trees of the following southern species harvested from among southern pines: 

 sweetgum, white oak, hickory sp., southern red oak, post oak, yellow-poplar, 

 black tupelo, water oak, chestnut oak, black oak, scarlet oak, and red maple. 



Cement (200 g) and 20-40 mesh wood (15 g ovendry weight) were dry-mixed 

 in a polystyrene cup. To this dry mix, 91 ml of distilled water was added and 

 kneaded for 5 minutes. The wood-cement mixture was placed into a 1-pt Dewar 

 flask, iron-constantan thermocouple wires were inserted through a cork into the 

 mixture, the flask sealed, and hydration temperature measured. The time to 

 obtain maximum temperature of hydration was considered as the required setting 

 time of the mixture. Four replications for each species of wood-cement mixture 

 were made, each representing a blend of breast-height samples from four trees (6 

 inches dbh) of each species. Hydration temperature (TE), time to reach maxi- 

 mum temperature rise (T2), and slope of the time-temperature curve were con- 

 sidered indicators of inhibitory characteristics of each species. To reduce 

 inhibition to set, matched specimens were boiled (treated) in distilled water for 6 

 hours; at 2, 3, 4, and twice at 6 hours, these wood particles were washed with 

 boiling distiUed water, and then collected and dried for evaluation as described 

 above. 



'^Moslemi, A., Y. Lim, and A. D. Hofstrand. 1982. Propensity of wood and bark from twelve 

 southern hardwoods to inhibit setting of wood, portland-cement, and water systems. South. For. 

 Exp. Stn., U.S. Dep. Agric, For. Serv., Fin. Rep. FS-SO-3201-26, dated February 26, 1982. 

 (Also, manuscript in preparation.) 



